Various different communication devices are well known and form a large part of our everyday lives. Examples of the well known wireless communication devices include walkie-talkies and other simple two-way radios, cellular phones, pagers, and Palm-type handheld devices that permit e-mail or Internet access. Simple two-way radios require no network infrastructure, since each radio communicates directly with each other radio. However, simple two-way radios also offer none of the network-based features people expect of a modern communications system, such as the ability to set up a private connection between two communications devices using an identifier such as a phone number or name. Each of the other examples given of communications devices requires an expensive network infrastructure to operate correctly.
One area where communication devices can play an important role is in the workplace, to allow mobile employees to communicate with one another. Many workplaces have already installed a wireless computer network to support wireless devices such as laptop computers. These wireless computer networks use a standard wireless networking protocol, such as one of the 802.11 standards, and consist of one or more wireless access points, typically installed in the ceiling of a building. The access points communicate with various wireless devices using the selected standard wireless networking protocol, and communicate with each other, and with other computers, over a standard wired computer network, such as Ethernet. Since a full-featured modern communication system requires a network infrastructure to operate correctly, it makes sense to develop a wireless communications system which uses a typical wireless computer network (such as one based on an 802.11 standard) as its network infrastructure. This makes it possible to deploy a wireless communications system without the need to deploy a completely separate parallel wireless network.
A desired feature of a communications system, especially one intended for use in the workplace, is the capability to allow multiple users to talk to each other as a group. Ideally, this feature would be easy to use, offer virtually instant response, and would not require one user to individually contact every other member of the group to initiate a communications session. Some wireless devices, such as walkie-talkies and some cellular phones, provide a feature with some or all of these characteristics. This feature is inherent in the way walkie-talkies operate, since any voice message transmitted by a walkie-talkie is heard by any other walkie-talkies nearby which are tuned to the same frequency channel. When this feature is provided on a communications system which does not use walkie-talkies, it is often patterned on the way walkie-talkies are used. The users place themselves in a special mode, and select which pre-defined group they wish to be a part of (this selection is roughly the equivalent of selecting the frequency channel on a walkie-talkie). Once the mode is activated, transmission of a voice signal to other group members is typically controlled with a single button, with the user pressing the button the entire time they wish to transmit. This type of multi-user communications session, based roughly on the push-to-talk mode found on typical walkie-talkies, will be referred to as a “chat” mode.
There are communications systems on the market which are based on a typical wireless communication network such as one of the 802.11 protocols, but these systems do not typically provide a chat mode. Implementing a chat capability in a voice communications system based on a typical wireless computer network, such as one of the 802.11 protocols, brings up several problems not typically encountered with walkie-talkies. These problems include power consumption, system latency, and a limitation on the rate that communications packets can be efficiently processed by the network.
A typical walkie-talkie does not consume much power while listening for communications. It can therefore be left in a listening mode, with its receiver turned on, the entire time it is being used, with no great penalty paid in battery life. In contrast, a wireless device based on a wireless computer network typically consumes significant power when listening for communications. The state of a typical wireless device intended for use with a wireless computer network is therefore changed whenever incoming communications signals are not expected, with the receiver turned off most of the time to reduce power consumption. This power management has the side effect of adding significant latency to the system when incoming signals actually arrive. It takes time for each device to realize new communications are coming in, and to change its state back to a listening state, with the receiver turned on. This added system latency, if it occurred each time a member of a chat group started transmitting a voice signal, would defeat the intended purpose of the feature, which is to provide easy-to use instant communication between group members.
An additional complicating factor is the network limitation on the rate that communications packets can be processed and delivered by the network. For any system based on a typical computer network, all communications signals will be placed into packets based on the well-known Internet Protocol (IP). The wireless access points and various components of a typical wired computer network must process each of these IP packets separately, and there is a limit to the rate at which packets can be efficiently processed. The standard IP packet is transmitted from one transmitting device to a single receiving device, and is called a unicast packet. If a chat mode communications session involved a large number of users, and each user's device communicated with each other device using unicast packets, the rate of transmitted packets could easily grow too large. Because of this, it is desired that the chat feature be implemented as much as possible using a different type of packet called a multicast packet, which allows one transmitting device to send the same single packet to multiple receiving devices, greatly reducing the total number of packets which must be processed by the network. However, the use of the multicast packet complicates the tradeoff between power consumption and system latency described above, because a device that has changed its state to the low-power state, with its receiver off most of the time, typically ignores multicast packets on the network. Failure to ignore multicast packets can significantly increase power consumption in this low-power state. Therefore, if optimum power consumption is to be achieved in the low-power state, only a unicast packet can reliably be counted on to reach the device and “wake it up”, returning it to the full listening state. Thus, a wireless communication device that is based on a typical wireless computer network, provides a chat capability, resolves the tradeoff between power consumption and latency, and which primarily uses multicast packets to implement the feature without increasing power consumption, is desirable. It is to this end that the present invention is directed.